It is known that certain materials will change their color and their ability to transfer light under the influence of an electrical field. This property is widely used in liquid crystal display electronic devices such as watches. However, the material is relatively expensive and has not been generally applied in greenhouses or other buildings. It has also been suggested that certain chemicals will reversibly change their state and their light transmission properties with changes in temperature.
A series of patents has issued which indicate that certain specific organic chemicals will reversibly change their state and their light transmission properties with changes in temperature. These patents indicate that specific organic polymers will, at a "cloud point", go into, or out of, solution when their temperature is raised. At their cloud point, when they are deposited out of the solution, the color or light transmission will change. However, commercially these materials have not been incorporated in flexible plastic resin films.
In U.S. Pat. Nos. 3,953,110 and 4,307,942 to Day Charoudi, a temperature responsive visible radiation control, polyvinylmethylether (PVME) is ". . . incorporated into a gel matrix by crosslinking or applied as an emulsion in a paint"(U.S. pat. No. 3,953,110, column 4, lines 54-56). Charoudi uses PVME and "cross linked hydroxyethyl methacrylate-hydroxyethyl acrylate copolymer" as the "gel or matrix" (U.S. Pat. No. 4,307,942, column 3, lines 44-53). In U.S. Pat. No. 4,260,225 to Walles a cloud-point polymer, i.e., having inverse solubility with a temperature rise, based on N-vinyl-5-methyl-2-oxazolidinone (PVO-M).
In a greenhouse, when the temperature rises past a certain point, the plants may be damaged. It would be useful if the greenhouse wall could change its light transmission property at a predetermined temperature point to avoid an excessive amount of sunlight from entering the greenhouse and raising its temperature. Similarly, in other buildings, if the windows or walls could reflect more sunlight, at a predetermined rise in ambient temperature, it may be possible to reduce the air conditioning load, control the sunlight entering the building or, in other ways, improve the building's functions.